Imaging system and associated method for surveying underwater objects

ABSTRACT

A system for surveying an underwater topography includes an ultrasonic sensor array disposable in physical contact with a body of water for generating electrical signals encoding ultrasonic echo responses of underwater objects in the body of water. The sensor array includes a plurality of electromechanical transducers in turn including at least one electroacoustic transducer and one acoustoelectric transducer. The transducers are disposed in a configuration extending in at least two dimensions. An a-c current generator is operatively connected to the electroacoustic transducer for energizing the electroacoustic transducer with an electrical signal of a pre-established ultrasonic frequency. Means are provided which operatively connected to the sensor array for determining locations of the electromechanical transducers relative to one another. A processor or computer is operatively connected to the sensor array for analyzing the electrical signals in accordance with the determined locations of the electromechanical transducers to determine surfaces of objects disposed at least partially in the body of water and for generating a video signal encoding an image of the objects. A video monitor is operatively connected to the processing means for displaying the image of the objects.

BACKGROUND OF THE INVENTION

This invention relates to an imaging system utilizing ultrasonic wavesfor sensing purposes. More particularly, this invention relates to sucha system for use in surveying an underwater topography. This inventionalso relates to an associated method.

Treasure hunters' first and sometimes primary chore is determining thelocations of valuable artifacts. A considerable number of archeologicalartifacts originating, for example, from ancient shipwrecks, remainunderwater. Formerly, efforts to locate such marine treasure entaileddiving with scuba gear or high pressure suits. More recently,submersibles and robotic cameras have been employed to scout for sunkenships.

Despite these modern solutions, the hunt for underwater artifactsremains impeded by the difficulty of detecting objects underwater whenavailable light levels are low. Such low light levels exist at greatdepths and in shallower waters where silt and other waterborne particlesscatter light. Of course, visual detection is completely impeded whereartifacts have been covered by sand or silt. Although ferrous artifactscan be located in such conditions with the aid of magnetic detectors,non-ferrous artifacts such as bronzes, pottery, gold and silver remainundetectable.

OBJECTS OF THE INVENTION

An object of the present invention is to provide an imaging system whichfacilitates detection of underwater objects.

Another object of the present invention is to provide such an imagingsystem which is unaffected by existing light levels.

It is a more specific object of the present invention to provide such animaging system capable of detecting objects inside other objects whichare underwater.

A further object of the present invention is to provide an associatedimaging method enabling the visual inspection of underwater objects evenat low ambient light levels.

These and other objects of the present invention will be apparent fromthe drawings and descriptions herein.

SUMMARY OF THE INVENTION

A system for surveying an underwater topography comprises, in accordancewith the present invention, an ultrasonic sensor network disposable inphysical contact with a body of water for generating electrical signalsencoding ultrasonic echo responses of underwater objects in the body ofwater. The sensor network includes a plurality of electromechanicaltransducers in turn including at least one electroacoustic transducerand one acoustoelectric transducer. The electromechanical transducersare disposed in an array which has at least two dimensions. An a-ccurrent generator is operatively connected to the electroacoustictransducer for energizing the electroacoustic transducer with anelectrical signal of a pre-established ultrasonic frequency. A positiondetermination element is operatively connected to the sensor network fordetermining locations of the electromechanical transducers relative toone another. A processor is operatively connected to the sensor networkfor analyzing the electrical signals in accordance with the determinedlocations of the electromechanical transducers to determine surfaces ofobjects disposed at least partially in the body of water. The processorincludes pattern recognition circuitry for comparing the determinedobject surfaces with a stored electronic library of stored surface datato identify the determined object surfaces as being consistent with apredetermined class of objects.

The system further comprises, in accordance with another aspect of thepresent invention, a position determination circuit operativelyconnected to the processor for determining locations of the determinedobject surfaces relative to a global frame of reference. A recordingcomponent is operatively connected to the processor and the positiondetermination circuit for recording locations of the determined objectsurfaces relative to the global frame of reference. Thus, the latitudeand longitude, as well as the depth, of a detected object of interestmay be recorded for future reference. The recording component mayinclude an electronic data store or, alternatively, a printer.

Where the underwater sensor network includes a carrier, with thetransducers being mounted to the carrier, the detection system furthercomprises one or more motors operatively connected to the carrier formoving the carrier through the body of water. The motors may be mounteddirectly to the carrier, in a self-propelled implementation, or to motormodules, or to a surface or submarine vessel which then drags the sensornetwork carrier through the body of water. The motor modules areprovided with wireless signal receivers for receiving instructions froma surface or underwater vessel.

The pattern recognition circuitry is operatively connected to the motoror motors for arresting the motors upon detecting that one of thedetermined object surfaces falls into a predetermined class of objectsof interest. Thus, if something of particular interest is detected,other investigations may be undertaken immediately to confirm theidentity and the importance of the find.

The processor may be located on the carrier itself or on a vessel whichis pulling the carrier through the body of water. Alternatively, theprocessor may be disposed at a more remote location, on land, at sea orin the air. In that case, the sensor network may be linked to theprocessor (and the processor to the motors) via a wirelesscommunications link.

The processor advantageously includes a video signal circuit generatinga video signal encoding an image of the determined object surfaces. Avideo monitor is then operatively connected to the processor fordisplaying the image of the determined object surfaces.

In accordance with further features of the present invention, theprocessor includes a view selector operatively connected to the videomonitor for selecting the image from among a multiplicity of possibleimages of the objects (different view angles or differentmagnifications, for example) and additionally includes a filter stageoperatively connected to the video monitor for eliminating a selectedobject from the image. The eliminated object may be overlie a selectedobject of special interest. Fish and undersea vegetation may be filteredout from a displayed image to view objects on the floor of the body ofwater. Alternatively, floor of the body of water may be filtered out iffish, bottom dwellers, plant life and/or other denizens of the deep arethe objects of interest.

The processor includes an analyzer operatively connected to theacoustoelectric transducer(s) for determining three-dimensional shapesof the objects by analyzing signals generated by the acoustoelectrictransducer(s) in response to ultrasonic pressure waves produced at theobjects in response to ultrasonic pressure waves produced by theelectromechanical transducer(s). The various components of theprocessor, including the analyzer, are realized in a general purposecomputer by generic processing circuits configured by programmedinstructions.

Where the electromechanical transducers include a plurality ofelectroacoustic transducers disposed in a predetermined array, theunderwater detection system further comprises means for energizing theelectroacoustic transducers in a predetermined sequence. Thus, theprocessor is able to associate any set of incoming reflected pressurewaves with the particular transducer which generated the pressure waves.The different transducer locations as well as multiple scanningoperations provide enhanced information for data processing purposes.This enables not only the refinement of the image (increased resolution)but also enables the selection (by the operator, usually) of differentview angles.

Where the electromechanical transducers include a plurality ofacoustoelectric transducers disposed in a predetermined array, theunderwater detection system further comprises means for receivingsignals from the acoustoelectric transducers in a predeterminedsequence. Because of this structure, the processor processes multiplesets of incoming reflected pressure waves each associated with theparticular sensor which detects the pressure waves. Again, the differentsensor locations as well as multiple scanning operations provideenhanced information which enables image refinement and the selection ofdifferent view angles. Of course, information utilized in imageprocessing is maximized where the sensor array includes multipledistributed pressure wave generators and multiple distributed pressurewave receivers.

The determination of transducer position may be implemented simply inthe case of a substantially rigid carrier. The electromechanicaltransducers are mounted to the carrier so that the locations of theelectromechanical transducers relative to one another are fixed by thecarrier. However, it is alternatively possible for the transducers to bedisposed at variable locations relative to one another. In that case,the instantaneous positions of the pressure wave generators and thepressure wave receivers relative to each other are determined byprocessing or analyzing additional electrical signals generated by thesensors or receivers in response to pressure waves transmitted throughthe body of water directly from the electroacoustic transducers orgenerators to the acoustoelectric sensors or receivers.

A method for surveying an underwater topography comprises, in accordancewith the present invention, steps of disposing an array ofelectroacoustic transducers in operative contact with a body of water,determining physical locations of the transducers relative to eachother, and energizing the transducers to generate a series of electricalsignals encoding echo responses of underwater objects in the body ofwater, the echo responses corresponding to a multiplicity of pressurewave paths from the transducers to each of the objects and back to thetransducers. The method further comprises a step of automaticallyanalyzing the electrical signals to determine surfaces of objectsdisposed at least partially in the body of water. This analyzingincludes the step of comparing the determined object surfaces with astored electronic library of stored surface data to identify thedetermined object surfaces as being consistent with a predeterminedclass of objects.

In accordance with another feature of the present invention, furthercomprises the steps of determining locations of the determined objectsurfaces relative to a global frame of reference, and automaticallyrecording locations of the determined object surfaces relative to theglobal frame of reference.

Where the transducers are mounted to a carrier, the method alsocomprises the step of operating a motor to move the carrier through thebody of water. The motor is automatically stopped upon detecting thatone of the determined object surfaces falls into a predetermined classof objects of interest.

In accordance with a preferred mode of operation, the method furthercomprises the step of generating a video signal encoding an image of thedetermined object surfaces, and displaying the image of the determinedobject surfaces. A selected object may be automatically eliminated fromthe displayed image, for purposes of facilitating the viewing of otherobjects I the image.

Where the electromechanical transducers include a plurality ofacoustoelectric sensors, the energizing of the transducers may includereceiving signals from the sensors in a predetermined sequence.

Where the image is selected from among a multiplicity of possible imagesof the objects, the method further comprises subsequently selecting adifferent image from among the possible images and displaying thedifferent image on the monitor.

An ultrasonic imaging system in accordance with the present inventionfacilitates detection of underwater objects, even when the ambient lightlevels are insufficient to allow visual inspection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially a schematic perspective view and partially a blockdiagram of a nautical ultrasonic imaging system in accordance with thepresent invention.

FIG. 2 is a block diagram showing components of a processing systemdepicted in FIG. 1.

FIG. 3 is a block diagram of a preliminary signal processing circuitillustrated in FIG. 2.

FIG. 4 is a block diagram of an ultrasonic waveform generator shown inFIG. 2.

FIG. 5 is a block diagram of a digital-to-analog converter shown in FIG.2.

FIG. 6 is a block diagram showing a specific variant of the system ofFIGS. 1 and 2.

FIG. 7 is a block diagram showing another variant of the system of FIGS.1 and 2.

FIG. 8 is a schematic perspective view of an ultrasonic pressure wavegenerating and/or sensing unit utilizable in an ultrasonic imagingsystem in accordance with the present invention.

FIG. 9 is a schematic perspective view of a carrier net and dedicatedpropeller units of a modified ultrasonic imaging system in accordancewith the present invention.

FIG. 10 is a schematic perspective view of a rigid carrier and dedicatedpropeller units of another modified ultrasonic imaging system inaccordance with the present invention.

FIG. 11 is a schematic perspective view of another rigid carrier oftransducers of an ultrasonic imaging system in accordance with thepresent invention.

FIG. 12 is a block diagram similar to FIG. 2 and containing additionalelements of a processor and of an ultrasonic imaging system inaccordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated in FIG. 1, a system for surveying an underwatertopography comprises an ultrasonic sensor array 12 disposable inphysical contact with a body of water BW. The sensor array generateselectrical signals encoding ultrasonic echo responses of underwaterobjects UO in the body of water BW. Sensor array 12 includes a pluralityof electromechanical transducers 14 exemplarily realized essentially bypiezoelectric wafers. Sensor array 12 further includes a carrier 16 suchas a net. Carrier net 16 is towed through water body BW by a boat BT viaa tow line 18. A multiple lead cable or wireless telecommunications link20 extends along tow line 18 and operatively connects transducers 14 toa processing system 22. Processing system 22 analyzes incomingelectrical ultrasonic signals arriving from transducers 14 and generatesa video signal encoding an image of an underwater topography includingone or more of the underwater objects UO. The video signal is fed to amonitor 46 for display of the image thereon.

Sensor array 12 and more particularly selected transducers 14 producemechanical pressure waves 24 of one or more ultrasonic frequencies.These outgoing pressure waves 24 are reflected from the underwaterobjects UO, as indicated at 26, and received by transducers 14. Theincoming pressure waves are converted by selected transducers of sensorarray 12 into electrical signals transmitted over cable or wirelesstelecommunications link 20 to processing system 22.

In order to optimize data production, transducers are disposed in aconfiguration extending in at least two dimensions. This configurationis determined in part by the attachment of transducers 14 to carrier net16.

As illustrated in FIG. 2, transducers 14 include a plurality ofpressure-wave-generating electroacoustic transducers 28 and a pluralityof pressure-wave-receiving acoustoelectric transducers or sensors 30.Transducers or wave generators 28 are arranged in a predetermined two-or three-dimensional configuration such as a V. Transducers or sensors30 also have a two- or three-dimensional configuration.

An a-c current or waveform generator 32 is operatively connected toelectroacoustic transducers 28 for energizing the electroacoustictransducers 28 with an electrical signal of a pre-established ultrasonicfrequency. Electroacoustic transducers or wave generators 28 areenergized one at a time, in a predetermined sequence, by the sameultrasonic frequency or by different ultrasonic frequencies.

Acoustoelectric transducers or sensors 30 are operatively connected viacable or wireless telecommunications link 20 and an analog-to-digitalconverter 36 to a digital processor 34. Processor 34 may be implementedby a general purpose computer specially programmed to realize thefunctional modules shown in FIG. 2. Processor 34 includes, as one suchmodule, a preliminary signal processing circuit 38 which analyzesincoming pressure waves 26 in accordance with the location of theparticular electroacoustic transducer 28 which generated the outgoingpressure wave 24 reflected by the underwater objects UP to produce theincoming pressure waves 26.

As illustrated in FIG. 3, preliminary signal processing circuit 38includes a circuit 40 for determining the positions of transducers 14relative to one another. Circuit 40 receives, via a lead or multiple 41extending from analog-to-digital converter 36, electrical signalsderived from the incoming pressure waves 26. Circuit 40 separates outthose signals corresponding to direct or unreflected ultrasonic pressurewave transmission paths to determine the relative locations oftransducers 14. The encoded locations of transducers 14 are communicatedby circuit 40 to a surfaces detection circuit 42. Circuit 42 analyzesincoming electrical signals from sensor array 12 to determine andanalytically define the surfaces of underwater objects UO which generatereflected pressure waves 26 in response to ultrasonic pressure waves 24(FIG. 1). Circuit 42 determines the three-dimensional shapes of theunderwater objects UO. A time base 43 enables operation of circuits 40and 42.

As shown in FIG. 2, preliminary signal processing circuit 38 isoperatively connected to a video signal generator 44. Partially inresponse to surface data from circuit 38, generator 44 produces a videosignal encoding an image of an underwater topography including selectedunderwater objects UO. Generator 44 is connected to video monitor 46 fordisplaying the underwater image.

Preliminary signal processing circuit 38 is operatively connected towaveform generator 32 via an outgoing signal control unit 48. Controlunit 48 produces a control signal which determines, for example, thefrequency of an outgoing ultrasonic pressure wave 24 and the identity ofthe electroacoustic transducer 28 generating that pressure wave.Waveform generator 32 comprises a variable-frequency ultrasonic signalsource 50 and a multiplexer 52, as illustrated in FIG. 4. Source 50 andmultiplexer 52 receive control signals via respective leads 54 and 56from control unit 48. Multiplexer 52 operates to connect signal source50 sequentially to different electroacoustic transducers 28. Typically,the energization sequence of transducers 28 is pre-established anddetermined in part by the specific configurations of transducers 28 andtransducers 30 on carrier 16. In many cases, in order to facilitate theseparation of incoming reflected signals 26 originating at differentelectroacoustic transducers 28, these transducers are activated withsignals of detectably different ultrasonic frequencies. The sequence oftransducer activation and the frequency or frequencies of actuation arecommunicated by control unit 48 to surfaces detection circuit 42.Detection circuit 42 utilizes that information to properly analyze thearriving ultrasonic signals. In the event that the incoming data isinsufficient for detection circuit 42 to isolate, calculate and definesurfaces of underwater objects UO, the detection circuit may transmit asignal to control unit 48 to change the energization sequence oftransducers 28 and/or the energization frequencies.

As illustrated in FIG. 5, analog-to-digital converter 36 includes amultiplexer 58 and digitization elements 60. Multiplexer 58 receives aswitching control signal via a lead 62 extending from control unit 48.Control unit 48 enables the decoding of incoming ultrasonic pressurewaves in a pre-established sequence. This sequence is determined in partby the configurations of transducers 28 and 30 and by the frequencies ofenergization. In addition, surfaces detection circuit 42 (FIG. 3) maycause control unit 48 to vary the signal reception sequence for purposesof enhancing resolution and surface detection.

FIG. 6 shows a specific configuration of an underwater-topographyimaging system including just one electroacoustic transducer 64 and amultiplicity of acoustoelectric transducers 66. Here the enhancement ofimage resolution and optimization of surface detection and definitionare accomplished mainly by varying the ultrasonic output frequency ofthe one electroacoustic transducer and the sequence of signaltransmission from sensors or acoustoelectric transducers 30.

FIG. 7 depicts a particular configuration of anotherunderwater-topography imaging system including just multipleelectroacoustic transducers 68 and a single acoustoelectric transducer69. In this case, the enhancement of image resolution and optimizationof surface detection and definition are accomplished by varying theultrasonic output frequencies and the energization sequence of theelectroacoustic transducers.

As shown in FIG. 8, an ultrasonic pressure wave generating and/orsensing unit 70 attachable, for instance, to a junction of differentstrands of carrier net 16 comprises a body or casing 72 and a pluralityof tubular directional elements 74 projecting in different directionsfrom body 72. Each element 74 is associated with a respectivepiezoelectric wafer or chip (not illustrated). Thus, a single locationon carrier net 16 may support a plurality of electroacoustic transducers28 and/or acoustoelectric transducers 30. However, there must be aplurality of locations on carrier net 16 which carry one or moreultrasonic pressure wave transducers 14.

As depicted in FIG. 9, a carrier net 76 for an ultrasonic sensor array78 may be provided with a plurality of self-contained motive orpropeller units 80. Units 80 are connected to net 76 via tension lines82 and have steering vanes 84, as well as propellers 86. Steering vanes84 and propellers 86 may be controlled from a remote location, forexample, a ship (not shown) either via a signal transmission cable (notshown) or via wireless signal transmitters and receivers (not shown).

Propeller units 80 are attached to carrier net 76 for applying a forcethereto relative to a body of water in which or one which carrier net 76is disposed. It is contemplated that an underwater disposition ofcarrier net 76, for example, below any surface wave action, would beoptimal for reducing stress on the carrier and for facilitating themaintenance of the sensor array 78 in a given configuration. Theorientations of propeller units 80 relative to carrier net 76 willchange, as indicated in phantom lines at 88, to lift carrier net 76towards the surface of a body of water after completion of a maritimescanning operation. It is to be noted that propeller units 80 can bedifferentially operated to translate carrier net 76 and the entrainedsensor array 78 in different directions, including up and down andparallel to an underlying underwater geologic surface. The orientationof carrier net 76 in a body of water may be changed to facilitatescanning and object detection operations.

FIG. 10 depicts a carrier 90 of rigid frame construction. Fastened tocarrier 90 are a plurality of ultrasonic pressure wave generating and/orsensing units 92. Carrier 90 may be dragged along a water surface orbeneath the surface by a dedicated propeller unit 94. Auxiliarypropeller units 96 may be tethered to carrier 90 for assisting the mainpropeller unit 94 in orienting the carrier and in raising and loweringthe carrier through a body of water. As discussed above, ultrasonicpressure wave generating and/or sensing units 92 are operativelyconnected to a processing system 22 (FIG. 1) via a cable or wirelesstransceiver components. In the embodiment of FIG. 10, the determinationof transducer position may be implemented simply and automatically byvirtue of fixation of the locations of the electromechanical transducers92 relative to one another.

FIG. 11 illustrates another transducer carrier 106 of substantiallyrigid construction. Carrier 106 includes a substantially cylindricalbody 108 with a pair of stabilizers 110 and 112. Stabilizers 110 and 112may be shiftable relative to body 108, by respective motors (notillustrated), for facilitating the steering of carrier 106 through abody of water WB. Carrier 106 is dragged through the water by a tensionline 114 connected to a back end of a surface vessel 116.

An array of electromechanical (electroacoustic and acoustoelectric)transducers 118 are mounted to carrier body 116 and optionallystabilizers 110 and 112 for picking up reflected pressure waves ofultrasonic frequencies from underwater surfaces. A signal transmissionline (not separately illustrated) extending along tension line 114 or awireless transmission link may be provided for carrying signals betweentransducers 118 and vessel 116. If carrier 106 is provided with motorsfor shifting stabilizers 110 and 112, control signals for those motorsmay also be carried by this transmission line.

Carrier body 108 may be enclosed and define one or more internalchambers. For example, carrier body 108 may itself be apersonnel-carrying submarine. In that event, a propeller 120 is locatedat the rear end of the carrier body 108.

As illustrated in FIG. 2, processor 34 includes a view selector module98 which is operatively connected to video monitor 46 for selecting adisplayed image from among a multiplicity of possible images ofunderwater objects UO. More specifically, view selector module 98operates in response to instructions from a keyboard 100 or a mouse 102to select a view angle and a magnification for the displayed image.Accordingly, a user may induce a change in the displayed image from oneview angle to another or from one magnification to another.

As further illustrated in FIG. 2, processor 34 includes a filter stageor object removal module 104 operatively connected to video monitor 46for eliminating a selected object or portion of an object from thedisplayed image. Modules 98 and 104 are incorporated into processor 34and are realized by generic computer circuits whose functions aredetermined by programming.

In surveying an underwater topography utilizing an imaging system asdescribed herein above, for instance, with reference to FIG. 1, thesensor array is disposed in operative contact with body of water BW,determining physical locations of the transducers relative to eachother, and energizing the transducers to generate a series of electricalsignals encoding echo responses of underwater objects in the body ofwater, the echo responses corresponding to a multiplicity of pressurewave paths from the transducers to each of the objects and back to thetransducers. The electrical signals are automatically analyzed togenerate a video signal encoding an image of the objects, the videosignal being fed to a video monitor to thereby display the objects onthe monitor.

FIG. 12 illustrates all of the elements shown in FIG. 2 and showsadditional components of processing system 22 and digital processor 34.In particular, a pattern recognition circuit or module 122 isoperatively connected to preliminary signal processing circuit 38 forpurposes automatically analyzing the surface data from circuit 38 toidentify types of objects located underwater. Pattern recognitioncircuit 122 consults a memory 124 which is loaded with data describingthe shapes of objects of various classes. The contents of memory 124 mayvary, depending on the purposes of underwater searching. For example,where the imaging system is used for antiquities hunting, memory 124contains encoded templates for ancient ships, columns, urns, statuary,and other objects known to be frequently transported via sea goingvessels. Where the imaging system is used for applications in marinebiology, memory 124 contains three-dimensional surface data describingthe shapes of different underwater life forms, which may include fish,mammals, crustaceans, jellyfish, squid, etc. In any case, where imagesof underwater target objects are to be shown on video monitor 46, objectremoval module 104 filters out those objects which are not selected asbeing of interest. Object removal module 104 may also consult memory124, either directly or indirectly via pattern recognition circuit 122,to determine which objects are to be displayed and which objects are tobe deleted from representation on video monitor 46. Of course, inputdevices such as keyboard 100 may be operatively connected to patternrecognition circuit 122 for purposes of enabling user selection ofobject classes of interest during any particular ultrasonic underwatersearch.

Processor 34 further includes a module 126 for determining a locationrelative to global coordinates (latitude, longitude, and sea or oceandepth). This module receives input from conventional navigationequipment (not illustrated). Coordinates module 126 and patternrecognition circuit 122 are connected to a storage or recording device128 such as a printer and/or to memory 124 for purposes of recording theidentity and location of any objects detected by pattern recognitioncircuit 122. Thus, a sensor carrier 16, 76, 90, 106 may move along asearch path while continually monitoring underwater objects andmaintaining a log of detected objects. Subsequently, a manned or roboticvessel may be dispatched to more closely inspect any located objects ofinterest.

In an alternative search mode, pattern recognition circuit 122 isconnected to motors 130 which propel the sensor carrier 16, 76, 90, 106.Upon detecting an object of possible interest, pattern recognitioncircuit 122 de-energizes motors 130, thereby maintaining the sensorcarrier in proximity to the objects while a closer or more completeinvestigation is undertaken.

It is to be noted that an ultrasonic transducer carrier 16, 76, 90, 106as described herein may be provided with various devices for protectingthe sensor array from marine creatures such as dolphins or sharks. Suchprotective devices could include chemical dispensers for releasingrepellants into the water. The ultrasonic pressure waves may inthemselves have a repellant effect, as with land animals such asrodents.

Although the invention has been described in terms of particularembodiments and applications, one of ordinary skill in the art, in lightof this teaching, can generate additional embodiments and modificationswithout departing from the spirit of or exceeding the scope of theclaimed invention. For example, sensor carriers 16, 76, 90, 106 may takevarious forms and shapes and may be provided with various ancillarydevices such as video cameras, manipulating arms, storage compartmentsfor objects retrieved by such arms. Where the carrier is provided withdedicated motors, processor 34 may be provided with programs forfiltering out ultrasonic vibrations arising from the operation of themotors. Accordingly, it is to be understood that the drawings anddescriptions herein are preferred by way of example to facilitatecomprehension of the invention and should not be construed to limit thescope thereof.

What is claimed is:
 1. A system for surveying an underwater topography,comprising:ultrasonic sensor means disposable in physical contact with abody of water for generating electrical signals encoding ultrasonic echoresponses of underwater objects in said body of water, said sensor meansincluding a plurality of electromechanical transducers in turn includingat least one electroacoustic transducer and one acoustoelectrictransducer, said electromechanical transducers being disposed in anarray which has at least two dimensions; an a-c current generatoroperatively connected to said electroacoustic transducer for energizingsaid electroacoustic transducer with an electrical signal of apre-established ultrasonic frequency; position determination meansoperatively connected to said sensor means for determining locations ofsaid electromechanical transducers relative to one another; andprocessing means operatively connected to said sensor means foranalyzing said electrical signals in accordance with the determinedlocations of said electromechanical transducers to determine surfaces ofobjects disposed at least partially in said body of water, saidprocessing means including pattern recognition circuitry for comparingthe determined object surfaces with a stored electronic library ofstored surface data to identify the determined object surfaces as beingconsistent with a predetermined class of objects.
 2. The system definedin claim 1, further comprising:additional position determination meansoperatively connected to said processing means for determining locationsof said determined object surfaces relative to a global frame ofreference; and a recording component operatively connected to saidprocessing means and said additional position determination means forrecording locations of said determined object surfaces relative to saidglobal frame of reference.
 3. The system defined in claim 2 wherein saidrecording component includes an electronic data store.
 4. The systemdefined in claim 2 wherein said recording component includes a printer.5. The system defined in claim 1 wherein said underwater sensor meansincludes a carrier, said transducers being mounted to said carrier,further comprising motor means operatively connected to said carrier formoving said carrier through said body of water.
 6. The system defined inclaim 5 wherein said pattern recognition circuitry is operativelyconnected to said motor means for arresting said motor means upondetecting that one of said determined object surfaces falls into apredetermined class of objects of interest.
 7. The system defined inclaim 5 wherein said motor means is mounted to said carrier so that saidcarrier is self-propelled.
 8. The system defined in claim 5 wherein saidmotor means is mounted to a vessel, said vessel being tied to saidcarrier.
 9. The system defined in claim 1 wherein said processing meansis operatively connected to said sensor means via a wirelesscommunications link.
 10. The system defined in claim 1 wherein saidprocessing means includes a video signal circuit generating a videosignal encoding an image of said determined object surfaces, furthercomprising a video monitor operatively connected to said processingmeans for displaying the image of said determined object surfaces. 11.The system defined in claim 10 wherein said processing means includes aview selector operatively connected to said video monitor for selectingsaid image from among a multiplicity of possible images of said objects.12. The system defined in claim 10 wherein said processing meansincludes a filter stage operatively connected to said video monitor foreliminating a selected object from said image.
 13. The system set forthin claim 1 wherein said processing means includes analyzing meansoperatively connected to said acoustoelectric transducer for determiningthree-dimensional shapes of said objects by analyzing signals generatedby said acoustoelectric transducer in response to ultrasonic pressurewaves produced at said objects in response to ultrasonic pressure wavesproduced by said electromechanical transducers.
 14. The system definedin claim 1 wherein said electromechanical transducers include aplurality of electroacoustic transducers disposed in a predeterminedarray, further comprising means for energizing said electroacoustictransducers in a predetermined sequence.
 15. The system defined in claim1 wherein said electromechanical transducers include a plurality ofacoustoelectric transducers disposed in a predetermined array, furthercomprising means for receiving signals from said acoustoelectrictransducers in a predetermined sequence.
 16. The system set forth inclaim 1 wherein said position determination means includes asubstantially rigid carrier, said electromechanical transducers beingmounted to said carrier so that the locations of said electromechanicaltransducers relative to one another are fixed by said carrier.
 17. Amethod for surveying an underwater topography, comprising:disposing anarray of electroacoustic transducers in operative contact with a body ofwater; determining physical locations of said transducers relative toeach other; energizing said transducers to generate a series ofelectrical signals encoding echo responses of underwater objects in saidbody of water, said echo responses corresponding to a multiplicity ofpressure wave paths from said transducers to each of said objects andback to said transducers; automatically analyzing said electricalsignals to determine surfaces of objects disposed at least partially insaid body of water, said analyzing including comparing the determinedobject surfaces with a stored electronic library of stored surface datato identify the determined object surfaces as being consistent with apredetermined class of objects.
 18. The method defined in claim 17,further comprising:determining locations of said determined objectsurfaces relative to a global frame of reference; and automatiallyrecording locations of said determined object surfaces relative to saidglobal frame of reference.
 19. The method defined in claim 17 whereinsaid transducers are mounted to a carrier, further comprising operatinga motor to move said carrier through said body of water.
 20. The methoddefined in claim 19, further comprising automatically stopping saidmotor upon detecting that one of said determined object surfaces fallsinto a predetermined class of objects of interest.
 21. The methoddefined in claim 17, further comprising generating a video signalencoding an image of said determined object surfaces, and displaying theimage of said determined object surfaces.
 22. The method defined inclaim 21, further comprising automatically eliminating a selected objectfrom said image.
 23. The method defined in claim 17 wherein saidelectromechanical transducers include a plurality of acoustoelectricsensors, the energizing of said transducers including receiving signalsfrom said sensors in a predetermined sequence.
 24. The method defined inclaim 17, further comprising selecting said image from among amultiplicity of possible images of said objects, further comprisingsubsequently selecting a different image from among said possible imagesand displaying said different image on said monitor.
 25. A system forsurveying an underwater topography, comprising:sensor means disposablein physical contact with a body of water for generating electricalsignals encoding echo responses of underwater objects in said body ofwater, said sensor means including a plurality of electromechanicaltransducers in turn including at least one electroacoustic transducerand one acoustoelectric transducer, said electromechanical transducersbeing disposed in an array which has at least two dimensions; an a-ccurrent generator operatively connected to said electroacoustictransducer for energizing said electroacoustic transducer with anelectrical signal of a pre-established frequency; position determinationmeans operatively connected to said sensor means for determininglocations of said electromechanical transducers relative to one another;and processing means operatively connected to said sensor means foranalyzing said electrical signals in accordance with the determinedlocations of said electromechanical transducers to determine surfaces ofobjects disposed at least partially in said body of water, saidprocessing means including pattern recognition circuitry for comparingthe determined object surfaces with a stored electronic library ofstored surface data to identify the determined object surfaces as beingconsistent with a predetermined class of objects.
 26. The system definedin claim 25, further comprising:additional position determination meansoperatively connected to said processing means for determining locationsof said determined object surfaces relative to a global frame ofreference; and a recording component operatively connected to saidprocessing means and said additional position determination means forrecording locations of said determined object surfaces relative to saidglobal frame of reference.